1. Field of the Invention
The present invention concerns a method for virtual adaptation of an implant to a body part of a patient.
2. Description of the Prior Art
Today prostheses or implants that are inserted into patients are often used in surgery, in particular in orthopedic surgery. Strictly speaking, prostheses are normally replications or replacements for body parts of a patient; implants are mainly abstract components such as, for example, plates or screws. For simplification, however the term “implant” will be used herein to encompass both implants in the actual sense as well as prostheses.
It is important to insert the implants into the patients with optimally exact fit and to optimally plan their insertion and to select a suitable implant for the insertion. Techniques derived, for example, from computer aided design (CAD) are increasingly required and utilized in the medical field for this purpose.
In the predominant number of cases, conventional (also film-based) x-ray exposures and hardcopy blueprints of implants represent the basis of a surgical planning. Construction or adaptation is done manually, virtually with pencil and tape measure, in order to find an optimal correct fit. Systems in which the x-ray image and/or the scale drawing of the implant already exist digitally represent an advance, but this case is predominantly limited to two-dimensional representations.
The geometries of the implants nearly exclusively exist only in 2D coordinates. Medical imaging, for example on the basis of computer tomography or the 3D C-arm technique, increasingly ensues in 3D. There are therefore newer approaches that describe concepts that also support the planning in three dimensions. These known techniques, however, are not very suitable for use in a procedure and that is only two-dimensional, and they do not proceed automatically, least of all for repositioning (i.e. the reconstruction of, for example, a fragmented bone after a fracture).
An example is U.S. Pat. No. 5,769,092, which discloses how bone cement can be removed in a computer-aided manner in order to replace an old prosthesis with a new one. Only standard representations parallel or orthogonal to the DICOM coordinate system are described therein, and the method is purely interactive, meaning that no automatic adaptation (for example of an implant in a bone) ensues based on pattern recognition.
Similar considerations apply to DE 43 41 367 C1, wherein interactive adaptation is likewise described. The article by K. Verstreken et al., “An Image-Guided Planning System for Endosseous Oral Implants”, IEEE Tran. Med. Im. Vol. 17, No. 5, October 1998 concerns improvements in 2D planning using 3D information. The primary emphasis therein is the use of automatic 3D contour and surface determination (segmentation), which ultimately is used again only in the basically 2D-oriented, interactive planning followed by 3D visualization and monitoring.
EP 0 093 869 A1 describes relatively briefly how individual prostheses and implants can be produced with an exclusively layer-based, slice-oriented method. For this purpose, it is proposed (without describing the technical realization in detail) to connect the layers (slices). From a modern point of view this is trivial and is limited to a procedure parallel to the table feed of the computed tomography apparatus. It is not described how 3D object adaptation can be implemented in free orientation with high resolution, and there is no consideration of how the adaptation can be implemented automatically, or how the adaptation can be supported by simultaneous complementary displays freely oriented in space.
WO 98/14128 likewise describes a method in the field of computer-aided prosthesis planning. This again is a predominantly two-dimensional approach: although (3D) CT input data exist, the adaptation ensues in two-dimensional slices (cross-sections). Nothing is said about how a positioning in isotropic space can be automated.